Manufacture of cement



June 6, 1939. HI BREER-WOOD El AL I 2,161,010

MANUFACTURE OF CEMENT Filed Sept. 10, 1957 CRUDE ROCK FIG. I. A M

OVERFLOW RAKE PRoDucT i I WI CONDITIONING ROUGHER FLoTATIoN CONCENTRATE TAILING RTLEANER FIDTATIDNI ITHICKENERI I I I CONCENTRATE TAILING IKILN OR BLENDING TANKS] I A WASTE CRUDE ROCK FIG. 2.

RAKE PRoDucT Bow. CLASSIFIER OVERFLOW RAKE PRODUCT CONDITIONING ROUGHER FLOTATION I I v CONCENTRATE TAILING I V CLEANER FLOTATION] UHIcKEIIERHTIIIcKENEfl CONCENTRATE TAILING' I WASTE BLENDING TANKS HINVEIgIT OHN C. WILLIAMS.

Patented June 6, 1939 MANUFACTURE Oi CEMENT Charles H. Breerwood, Narberth, and John C.

Williams, Gatasauqua, Pa., assign'ors to Separation Process Company, a corporation of Delaware Application September 10,1937, Serial No. 163,304 18 Claims. (Cl. 209-167) This invention relates to. the froth flotation treatment of cement raw materials and moretive ion, is employed to concentrate the'siliceous minerals, and in most cases to effect a differential flotation thereof.

It is among the purposes of the invention, and particularly in view of the low commercial value of Portland cement, to beneficiate inferior raw materials in a process involving a minimum of equipment, a minimum of processing steps, and especially with a minimum consumption of a reagent of an unusual class, as the reagents'of this class are inherently considerably more expensive than the fatty acids, or reagents based upon fatty acids, used heretofore in the treatment of such materials in processes in which the oxide mineral, calcite, is concentrated'in the flotation froth.

In contrast t'othe earlierprocesses, the concentrates of the present method are the waste or by-product minerals, and the flotation tailings are the useful minerals. Depending upon the natural-composition of the available material, the tailings may constitute the ultimate raw material mixture, properly corrected as to the proportions and ratios of the four essential constituents, or will form the major proportion of a mixture to be completely corrected by the addition of a quantity of another material, as when the natural material is deficient in an essential constituent to a degree that its recovery by flotation would involve an unnecessary and uneconomical waste of useful minerals, or when the material is above composition in its proportion of calcite, but excessive in a siliceous mineral and must. be beneficiated' whereby it may be used as a component. of a-mixture inwhich a siliceous material, such as a clay or a shale is theother.

The inferior natural raw materials contemplated herein are of almost infinite variety by reference both to mineralogical and physical composition, i. e., degree of recrystallization. As Portland cements are produced by combining oxides of silicon, iron, aluminum and calcium, the mineral sources of these oxides are of little practical efiect in the clinkering reactions provided mixture and contact is complete, but the natural mineral constituents have a very decided bearing upon the processing steps that may be adopted to eliminate excessive quantities of one or more minerals, i. e., quantities that will result in a mixture, or mixture component, corrected chemically within desirableor permissible limits.

The principal mineral constituents, of the materials with which this invention is-concerned, are calcite; silica in crystalline and cryptocrystalline forms, usually quartz, flint and/or chalcedony; alumina, which always occurs in practical quantities in the form of silicates of alumina, principally the various micas, but also as kaolin, kaolinite, the feldspar minerals, etc.; iron as oxides, the hydroxide, limonite and/or pyrite. usually present principally as dolomite, but also as magneslan alumino silicates, e. g., phlogopite mica, and/or brucite. Carbon, in a form commonly called graphitic is frequently present and although it has no apparent effect upon the clinkering reactions, it is highly undesirable in a specifically limited to and are to be construed in accordance with the following definitions.

S ilica refers to crystalline and crypto-crystalline silicon dioxide (3102) only; Silicate refers to any mineral salt of s'ilicic acids, particularly compounds containing alumina, magnesia or both. siliceous is generic and refers to either or both silica and silicate minerals as defined above.

Natural ci'sytallization of these mineral con' stituents, with the possible exception of the carbonaceous matter, occurs throughout extreme ranges, from large visible crystals down to materials of such incomplete orfine. crystallization that 'grinding'must be carried out to an extreme degree of -fineness torelease the physical bonds, or-at least to free a sufiicient proportion of the mineral or minerals occurring in excess, that the necessary elimination can be accomplished. An

Magnesia, an undesirable adulterant, is

exampleof the latter will be found hereinafter,

tion of tri-calcium aluminate at or near tion required grinding of the material to a slime, from which the principal concentrations of the silicates of alumina were accomplished in the particle size fractions below 20 microns.

Each of the materials described above may be beneficiated by the present method, and although an ancillary step or steps may be desirable or required to produce satisfactory results under specific conditions, to be described hereinafter,

With a few exceptions, the limestones, marls and chalks, available for cement manufacture, contain alumina in too great abundance for use in producing cements capable of satisfying the requirements of present specifications of the Federal and several State Governments, for cements of low heat of hydration, particularly specifications which fix a maximum limit for the propor- In many cases, and particularly in the materials available in the easterm cement producing dis- :tricts, the natural proportions of alumina are too, high to permit the production of cement of in erate heat of hydration, even when correcsa're added to the .materials. In some cases, d by compromise with theoretically desirtliga part of the alumina, and particularly Where the calcite content of the material is high enough 'to permit further correction of the ultimate composition by additions of high grade silica,-such as sandstone, where such correctives are ,available' Additions of iron oxides are not satisfactory or complete solutions of the problem, not

only because of their effect on the color of the concrete but principally because of the reduction of the silica ratio. Further, it is now generally i believed that substantial proportions of tetracalcium alumino ferrite decrease the resistance of concrete to attack by sulphates in marine and ground waters. One present specification limits the sum of tetra-calcium alumino ferrite and tricalcium aluminate in the finished cement to 10% and another specification sets a limit at 12%, and it will be evident that few natural materials can be utilized, by additions of iron'oxides, to produce compositions within these low limits. It should also be borne in mind that tetra-calcium alumino ferrite has little if any hydraulic value, and regardless of the beneficial effects of iron as a flux or catalyst in burning, this compound is an adulterant.

Magnesia, at least in quantities above a maximum limit, as established by various specifica- In general, the practice of the invention com- :'mixtures, the specification requirements can met by additions of iron oxide, to combine prises the flotation concentration of a minimum of the total weight of the raw materials, and when the composition of the materials permits, the flotation cell feed, relative to the total quantity of materials, is also limited to or near the minimum proportion that will permit ultimate correction of the total or final mixture. The minerals concentrated, and thereby eliminated, are the excessive quantities of the siliceous minerals, usuaully the silicates, whereby all but a minor quantity of the principal constituent of the ultimate mixture, namely calcite, is deposited as a flotation tailing, together with the useful quantities of the siliceous minerals and iron compounds, essential as constituents of the ultimate composition desired for burning.

One of the most important steps of the present methodv is the preliminary reduction of the natural materials by grinding. This step is not comparable either to customary cement raw material grinding, as the recovered mineral particles may have to be further reduced to make them suitable for burning, or to normal grinding as a preliminary to flotation separation by other processes and for the recovery of other minerals. In normal preliminary grinding prior to froth flotation concentration, the objective is to reduce the mineral bonds to a degree that a maximum recovery of high grade concentrate can be obtained. In the present method, however, th minerals are preferably reduced only to a degree that will permit the necessary elimination by flotation, for chemical and economical reasons, and especially when the materials are fine grained. At such a degree of grinding, it will be evident that a substantial proportion of the particles in the flotation tailings are unbroken, i. e., they are comprised of two or more distinct minerals, and it will be understood that a minimum proportion of thetotal mineral weight has been subtracted from the flotation pulp as a concentrate.

The chemical purposes of this procedure have primarily to do with the conditions under which the clinkering reactions take place. Only a relatively small proportion of the materials enter a liquid phase in the course of burning, and it is accordingly essential, in addition to the necessary fineness, that the minerals from which the four essential oxides are derived bethoroughly mixed and in intimate contact, for uniformity and completeness of the reactions. Provided the mineral particles are sufficiently fine, the proportion of unbroken or composite mineral particles, above described, are especially desirable as the mineral bonds assure contact of different constituents. Accordingly, further reduction is chemically undesirable, and it also will be realized that by subtracting a minimum of the total weight that the natural blend and contact of the original materials, and which has been improved by the mixing effect of grinding, has been disturbed only to a degree that will enable chemical correction of the composition.

As'grinding is one of the most expensive-operations in the manufacture of cement, it will be evident that substantially complete grinding of fine grained materials is economically impractical, and even in cases where the crystallization is relatively coarse, it will be obvious that mineral eliminations should be made without wasting power by unnecessarily reducing the quantity to be discarded.

The proportion of the total lime-bearing material to be treated by froth flotation depends upon both its mineralogical and chemical compositi n, especially the deviation from the desired composition, and the size ranges of natural crystallization. It is desirable, for purposes of economy, to. limit the quantity of flotation cell feed to the proportion of the total quantity which will permit correction of the mixture, when the flotation tailings and the remainder or the untreated part are mixed in proper proportions. Any such division is preferably made on a basis of particle size, rather than a mere division of the ground materials, to improve the results of .the' flotation operations and to economize .equipment and reagents.

,Thus, if the crystals are relatively coarse, and a suflicient proportion of the siliceous matteror mineral is freein the coarser fractions resulting from a limited degree of grinding, the next step is to classify the ground materials to segregate a chemically permissible maximum of the finer particle size fractions, and to subtract the siliceous matter only from the coarser fractions by flotation. This also enables -the chemist to discard the undesirable proporthe ground materials are preferably classified into slimes, intermediate and coarse fractions. The intermediate sizefractions are treated by froth "flotation and their tailings combined with quantities of the slimes and coarse fractions, the latter usually being first re-ground.

Usually, the material to be eliminated in part is micaceous, and although natural crystallization may be relatively coarse, the ease with which mica is reduced by grinding, as compared with the harder minerals, tends to concentrate a greater proportion of mica in the finer particle size fractions. Even in such cases, the proportion of the flotation cell' feed may be limited by preliminary classification, but the finer fractions are subjected to flotation, and their tailings utilized in combination with the untreated coarse fractions. It isto be understood that although the term coarse. has been used to describe these materials, the, ground materials are largely slimes, as the term-is used in. the art of flotation, or the proportion of slimes is'far too great to make it practical to discard them, andthe improvement in composition of the coarser fractions ordinarily is not complete and recombination with the flotation tailings is necessary to make the ultimate correction.

However, the more common materials avail able, especially in the "eastern cement producing districts, and which may be beneficiated for use in' the production of cement of the types described, require flotation treatment preferably of the entire supply. These materials are argillaceous limestones in which re-crystallization is so incomplete that extremely fine grinding must be resorted to to free a suflicient proportion of the micaceous matter, particularly sericite, to

make it possible to effect the desired corrections.

particle size makes it necessary to grind the total quantity to such fineness that the resulting materials are slimes. The actual or principal flotation separations are made in the particle size fractions below 20 microns, in the first three examples to be given hereinafter, and as at this degree of fineness, hydraulic classification is unnecessary, preferably the entire supply of ground materials are subjected to flotation. However, the process is'economical and competitive because only a minor part of the total weight is collected in the flotation concentrates, in contrast to the large calcite weight recovery in the concentrates of fatty acid flotation operations. The flotation tailings contain large proportions of unbroken rock particles, which for reasons previously discussed, are especially desirable to promote uniform and complete reactions in burning. 7

The flotation step of the process is carried out in the presence of a reagent, the surface active portion of which is a positive ion such as those of the class discovered by Lenher and described in his Patent No. 2,132,902, for a "Flotation process. The reagents found to be eifective are those which in solution give a positively charged ion containing an aliphatic hydrocarbon group of at least 8 carbon atoms, preferably quaternary ammonium compounds containing a hydrocarbon group of from 12 to 18 carbon atoms wherein the aforesaid constituents in solution give a positively charged ion, preferably the negative ion in solution being a halogen.

Of the foregoing class, two have been found to be especially satisfactory for the present purposes, and in the orderof preference are, first, dodecyl amine hydrochloride, hereinafter referred to for brevity as C-1, and second, a

mixture of hydrochlorides of the higher primary aliphatic amines in which the alkyl groups correspond in carbon content and composition to the fatty acids occurring naturally in coconutv oil, hereinafter referred to for brevity as 0-2. We have discovered, and it is an important feature of the practice of the invention, that although these reagents have capacity to collect operations are controlled, as will be illustrated by "the examples to be described hereinafter.

We have succeeded in effecting differential concentrations in the following order, flrst,'the aluminum and magnesian micas, second, the feldspar minerals, and third, crystalline silica, particularly quartz, without concentrating a substantial proportion of the free calcite grains in the froth. The practical significance of this discovery will be understood if it is remembered that the more common materials are excessive in alumina, and usually excessive in silica, and when present in substantial proportions magnesia is an undesirable adulterant. Thus, a very limited concentration of the total weight of the common materials effects the desired reduction of alumina, and as it occurs as a silicate, the

total silica is necessarily reduced, in the flotation tailings. Particularly when magnesian mica is present, this concentration effects desirable reductionsin alumina, silica and magnesia, retaining in the tailings the calcite and the usually desirable crystalline silica. Iron oxides tend to concentrate but as the collecting power of these reagents is relatively-low with respect to the oxides of iron, as well as calcite, froth cleaning by flotation, without the addition of collecting reagents, is effective in increasing the recovery in the flotation tailings. The unbroken rock particles are not as amenable to concentration, in the presence of these reagents, as the crystalline silica and can accordingly be retained in the tailings.

The differential separations are effected by conditioning the pulp with very limited quantities of the collecting reagent, and in light stage oiling circuits in which the total quantity is introduced in small increments. It will be understood that the term oiled is used to identify the flotation cell circuit, as the reagents are not oils. Especially in the treatment of fine pulps, the reagent is preferably diluted in a substantial volume of water to obtain accuracy in the control of each quantity introduced, and to effect rapid and complete dispersion in the relatively enormous volume of the pulp. Failure to control the quantities and dispersion of the reagent results in partial over-oiling and consequent partial heavy flocculation in which useful minerals are included. Expressed in another way, the concentrates are of low grade, unnecessary weight losses of the desirable minerals occur, the desired composition correction may not be com pleted, and the consumption of reagent makes the operation uneconomical.

Further, lower weight losses of the finer particles of the useful minerals are usually ob-- tained if the air volumes entering the pulp through the flotation cells are reduced below normal. The purpose in controlling the air volume is primarily to takeadvantage of the peculiar settling characteristics of mica particles. The shapes of the mica particles give them a much slower settling rate in water, the rate being about equal to particles of other minerals of half their diameter. Accordingly, although the surface effect of the collecting reagent upon the micaceous particles may be incomplete, the partial coating together with their low settling rates makes it possible to concentrate the mica with a negligible quantity of reagent.

The use of very small quantities of these reagents under-careful control in introducing and dispersing them in the pulp, as above described, results in the formation of siliceous concentrates of only a minor proportion of the total weight of the flotation cell feed. These are important features of the-invention, because under equiva lent conditions, the consumption of these expensive reagents in an inverted concentration is about one-fourth, and usually less, the consumption of fatty acids, or the fatty acid component of a reagent, required'to concentrate the calcite in the known processes, in which the concentrates represent a major proportion cf the weight of the feed. Accordingly, these features make the present method economically competitive with the older processes, despite thefact that the positive ion reagents cost several times as much .as the fatty acids, per pound. Calcite .pulps, of the class contemplated herein, are slightly alkaline, the normal alkilinity usually being within the range pH 7.4 to 7.8, and as the reagents specifically described are effective in alkalinepulps below about pH 8.5, no reagents need be employed to modify the natural alkalinity.

Further, the action of these reagents is notadversely affected by the use of depressing and dispersing agents, at least those of the types to be referred to hereinafter, when necessary to meet specific conditions. The limited quantities used permit the accurate control of froth volumes, at each stage, essential for the best results .in light stage oiling circuits, by suitable additions of common frothing agents, such as cresylic acid, but preferably a frothing agent comprising a mixture of branched and straight chain aliphatic monohydric alcohols boiling between about 152 C. and'about 162 C. obtainable along with methanol'by the catalytic hydrogenization of carbon oxides, hereinafter referred to for brevity as F4.

The practice of the invention can best be explained by reference to examples, which will serve as guides for the treatment of other inferior cement raw materials. The material selected for the three following examples is especially suitable for purposes of illustration, as it is especially difficult to beneficiate, and was generally believed to be not amenable to froth flotation concentration. The principal difficulties have to do with the extremely fine state of natural crystallization and the wide distribution or dispersion of colloidal or near colloidal graphitic carbon.

The material is typical of the finer grained argillaceous limestones of the Lehigh Valley cement producing district of Pennsylvania. It is classifiable geologically as Jacksonburg limestone of the Ordovician Age, and is intermediate in composition between limestone and shale, the color and general appearance more nearly resembling slate, but calcite is the most abundant mineral. The other principal minerals are quartz; mica, mostly of the sericite variety, dolomite, and iron, principally as the hydroxide, limonite.

calcite grains alternating with thin layers of fine scaly and fibrous sericite. There are occasional elongate lenses and elongated isolated grains of quartz. The quartz is widely distributed, usually as fine grains of a few microns or tens of microns in diameter. The carbonaceous matter is dispersed throughout the rock in intimate contact with the various other constituents, and constitutes about one half of one percent of the total mineral weight.

, Petrographic examination of this rock, after grinding to 98% minus the 325 mesh sieve, reveals that even in the particle size fractions below 20 microns, mineral bond breakage is incomplete, and that the coarser fractions are largely unbroken rock particles, i. e., the individual par ticles are composites of calcite, quartz and/or sericite. There is, however, a somewhat increased proportion of the mica in the finer fractions, in the form of free particles, and it is from the fractions below 20 microns that the principal concentrations are made. Carbonaceous inclusions and coatings of the calcite grains are frequent, and abundant on the quartz particles.

As will be seen from the analyses of the flotation cell feed in' the first two tables appearing hereinafter, the rock is unsuitable for cement manufacture without substantial correction. The

total silica and the alumina. are too high and the proportions of calcite and pure silica (quartz) are too low. The concentration and elimination of a part of the mica will effect the correction of both the silica and alumina, and increase the proportion of the calcite and quartz in the flotation tailings. This will be understood when it is realized that the weight ratio of silica to alumina in sericite mica is approximately 1.2:1.

The presence of carbonaceous matter even in proportions below 0.5%, inhibits successful concentration of the siliceous constituents of such materials. It has natural floatability and tends to flocculate and thereby concentrate a substantial proportion of the fine calcite and quartz grains, as well as other fine minerals,

thereby contaminating the flotation concentrates,

. rock, after normal preliminary reduction, was

ground in a tube mill in closed circuit with a bowl classifier, the rake sands being returned to the mill. The overfiowused as the flotation cell feed had the following average physical analysis:

, Per cent Plus 325 mesh plus 44 microns 1.50 Minus 43 microns plus, 28 microns 7.85 Minus 28 microns plus 22 microns 6.75 Minus 22 microns plus 15 microns 10.20 Minus 15 microns plus 10 microns 14.50 Minus '10 microns 59.20

- The objective of the first three examples was to derive a raw material mixture solely from this inferior material, i. e., without the addition of correctives, having a higher ratio of silica to total iron and alumina than could be obtained by addi-' tions of high grade limestone, and suitable to produce a general purpose Portland cement of high quality, allowance being mode for coal ash correction in burning.

First example The first example is intended to illustrate general principles in the application of the invention. "It was a batch flotation operation carried out in an 18" Fagergren flotation machine, this cell being large enough to produce results equivalent to practical commercial operations. It illustrates one of the preliminary alternative steps that maybe employed to make it possible to effect a satisfactory concentration of siliceous minerals in the presence of carbonaceous-matter. In this example, the carbonaceous matter was first removed by froth flotation.

The general conditions of the pulp were: .dilution 20% dry solids; temperature 72 F., and alkalinity normal at pH 7.8.

The carbonaceous matter was concentrated solely by alternate conditioning andflotation in the prerence of a frothing agent, F-1 identified above,- introduced in small increments until a total of 0.25 pound per ton of dry-solids had been added, the total flotationtime, being 7 minutes.

At the end of this time substantially all of the carbon had been eliminated.

As shown by the foregoing physical analysis, this pulp is a slime, and as colloidal. and nearcolloidal particles of the constituent minerals are abundant, natural flocculation is pronounced. As the floccules are aggregates of the various minerals, the natural-flocculation must be substantially reduced, to make effective separations possible. This may be accomplished by conditioning the pulp in the presence of a dispersing agent. Some of the common dispersing agents are ineffective, and others appear to promote,

flocculation, probably because of the wide variety jof minerals present in the pulp, but the lignin sulphonates, more fully described and claimed in Breerwood application Serial No. 163,303, filed September 10, 1937, are satisfactory.

The next step was therefore to disperse the natural flocculation, by conditioning the pulp for 3 minutes with 1.0 lb. of calcium lignin sul-- phonate.

This was followed by rougher concentration of the micaceous matter in alternate steps of conditioning and flotation, in the presence of dodecyl amine hydrochloride, C-l, as the collecting reagent. This collecting reagent was added as a 3% solution, to. obtain rapid and complete dispersion, in successive increments until 0.22 lb. had been introduced.

The rougher concentrates were then cleaned by froth flotation, without additional reagents, to deposit as tailings the uncoated and/or incompletely surface-coated quartz, calcite, iron minerals and unbroken rock particles, the cleaner flotation concentrates being the micaceous matter to be discarded as waste.

The principal flotation results were as follows:

Per- Analyses as percent Product cent SiO: weight ratio S10: F6103 A1303 C8003 Feed 100.0 16.24 1.88 6.48 69.60 1.94 Carbon 6.1 18.72 4.38 9.56 55.46 Cleaner cone- 10.0 33.28 2.35 17. 59' 35.69 Cleaner tails- 9. 7' 19.20 2.00 7.76 65.28 Rougher tails 74.2 13. 30 1.55 4.09 77.47 2.39

Combined tails-.. 83.9 13.98 1.60 4.52 76.2 2.28

It will be seen from the foregoing table that the final micaceous concentrates, produced by the collecting reagent, constituted only 10% of the total weight of the feed. The carbon concentrates involve a weight loss, but this was negligible and it will be seen that the alumina content was increased about 3% above that of the feed.

The fine quartz,-cssential in the final mixture, was recovered principally in the rougher tailings,

in which quartz constituted about two-thirds of, the total silica, having been accomplished by using only a limited quantity of the collecting reagent. The content of calcite was increased in the rougher tailings beyond the proportion desired for burning, and as the cleaner tailings were I of lower grade and about one-half of the total silica was quartz, the rougher and cleaner tailings were combined, thereby 'efiecting the desired ultimate composition correction, and providing a total weight recovery of 83.9%.

I It is especially to be noted that the addition of enough high grade limestone to increase the proportion of calcite from 69.6 to 76.2%, would not materially modify the unsatisfactory low silica ratio, but by the reduction of the. proportion of micaceous matter, the silica ratio of the combined rougher and cleaner tailings was 2.28.

For a better understanding of the complete practice of the invention, reference .is made to theapcompanying drawing in which: Fig. 1 is a 'fiow diagram, showing the preferred -method of treating the limestone described speciflcally in connection with the previous example, and materials substantially equivalent thereto, and

Fig. 2 is a slightly modified flow diagram, of advantage where the constituent or constituents occurring in excessive proportions are free in sufficient abundance in the finer fractions to make it practical to submit these fractions only to froth flotation.

Second example In the preferred procedure, illustrated in Fig. 1, the operations are continuous, and the second example corresponds to this flow of materials in pilot plant operation on a practical scale, in which the ultimate mixture was burned and ground to Portland cement, to demonstrate the practical advantages of the invention.

The crude rock, crushed to tube mill feed sizes, was ground in closed circuit with a Dorr bowl classifier, the rake product being returned to the mill for further reduction. This grinding circuit was adopted to make it economically practical to reduce the classifier overflow to the extreme fineness previously shown.

The average overflow included 340 pounds of dry solids an hour. The overflow was thickened in a Dorr thickener within a range from 18.5 to 19% dry solids for flotation feed. This pulp was then conditioned in a 24" Fagergren flotation machine, with the air supply permanently cut off, in the presence of a carbon depressing agent, this step being an alternative to the carbon concentration step described in the first example, and which has the advantage of making the carbonaceousmatter harmless to the subsequent flotation concentrations, although it is retained in the pulp, and the weight losses set forth in the previous table are avoided, as will beseen in the analyses to-be given hereinafter. The carbon depressing agent used was calcium lignin sulphonate, more fully described and claimed in Breerwood Patent No. 2,130,574, the quantity used being 2.10 pounds per ton of feed, this quantity being greater than necessary to depress the graphitic carbon, to employ the excess to disperse natural flocculation during the subsequent flotation operations, as more fully described and claimed in the co-pending application of Breerwood Serial No. 163,303, filed September 10, 1937. In addition to this agent, 0.25-pound of frothing agent F-l, and 0.44 pound of commercial No. 3 fuel oil per ton were added to the pulp during the conditioning period in this cell.

The conditioned pulp, continuously discharged, wasthen subjected to rougher concentration in a series of five 18" Fagergren flotation machines, in which the air volumes induced were restricted for reasons previously described. The collecting reagent employed was positive ion reagent 0- identified specifically above. It was introduced in 5% solution in water to efiect rapid and complete dispersion in cold water for the pulp and was added in stages to the flotation machine used as the conditioner and to 'each of the five rougher cells. The total quantity required to complete rougher concentration was 0.46 pound per ton.

The concentrates were, cleaned by froth flotation, without additions of reagent in three 18" Fagergren cells, the tailings of which were returned in continuous closed circuit, as middlings, to the conditioning cell. The cleaner concentrates included the proportion of mica to be eliminated, and were, accordingly, the waste products of the process.

The rougher tailings were correct in composition, for the production of a modern cement o general purposes, and were thickened to normal cement slurry densityin a Dorr thickener and burned in an oil fired kiln.

The principal analyses are given below, and it is especially significant that these results were obtained at average pulp temperatures of 55 F.

It will be seen from the analyses given above that the total weight loss has been improved, due principally to the effect of calcium lignin sulphonate in depressing the carbonaceous matter, and dispersing natural flocculation. The composition and silica ratio of the tailings are satisfactory for the production of high quality general purpose cement. It is to be noted that, although there is little if any magnesian mica in this material, the magnesia was not concentrated in the tailings, and that the final proportion is even less than in the feed. As a slight modification of this procedure, the middlings may be reground, to release more of the mica and again subjected to flotation in the rougher circuit.

Third example By reference to Fig. 2, it will be seen that it is of advantage to submit to flotation less than the entire supply of materialsto economize in reagent consumption and flotation cell equipment.

The extreme degree of fineness, to which the material of the foregoing examples must be reduced, does not make the treatment of a limited proportion substantially more economical than flotation of the entire supply in the manner described in the second example. However, this parallel but partially alternative method will be described specifically in its application to the same material for the sake of brevity.

The grinding circuit was arranged so that the classifier over-flow equalled 77% of the total ground materials, the fineness being substantially identical to the physical analysis given above, namely with 98% minus 325 mesh. The classifier overflow was the flotation cell feed. The rake sands from the classifier were the remaining 23% of the original weight of material. These sands were not subjected to flotation, but as the fineness was minus 50 mesh with 15% minus 325 mesh, they were reduced to suitable cement slurry fineness by separate closed circuit grinding, thickenedand finally mixed with the flotation tailings to be described hereinafter.

The tendency of the mica to become concentrated in the finer fractions, as previously described, caused an increase in the silica ratio of the coarser fraction, i; e., the rake sands, to 2.2, although the proportions of calcite and total silica did not change materially from those of the original material, being approximately oil-set by increased concentration of quartz in the coarser fractions.

The finer fractions were subjected to conditioning for carbon depression, dispersion of flocculation, and froth flotation, with the same reagents, as described in the second example. The total reagent consumption was decreased, approximately proportionally to the relative weights of the materials treated. The flotation results were slightly less effective in view of the greater proportion of mica in the feed, and the use of the.

same proportion of collecting reagent. The recombination of theflotation tailings and the ground rake sands resulted in a raw material mixture, corrected as to the proportion of calcite and with a satisfactory but somewhat low silica ratio of 2.02.

It is to'be understood that the methods of the second and third examplesarecontinuous, and

. that the objective was to produces useful composition from an available materialwithout additions of correctives obtained from. another source. However, it is to be understood that the grades. of the tailings can be modified by changing the quantities of the collecting reagent whereby final correction can be completed, or a I modified type ofcement may be ultimatelyv produced, by additions of quantities of .available correctives. It is also to be realizedthat the proportion of the total material treated, as in the third example, directly'aflfects the final composif tion, and that latter may also be modified by varying the proportions re-comhined, and further by additions of correctives.

' Fourth example This example is not illustrated in the drawing,

as the procedure closely parallels that previous- 1y described, and will be clearly understood from the following description.

The purpose of the example is to explain a more economical procedure that may be adopted when the mineralogical andphysical nature of the material permits eliminationof the finest fractions from the flotation cell feed. The presence of colloids, particles having colloidal be havior and those of extremely slow settling rates in water, seriously complicates the difflculties in making effective separations by flotation. These difliculties, in. 'pulps of the types contemplated herein, may be attributed to colloidal coating of mineral'grains, pronounced tendency of these fine minerals to flocculate naturally, and the liabilityof particles of slow settling rates to become trapped in the froth, even though theymay not be substantially surface-coated by the collecting reagent.

The flotation of the. relatively. coarser fractions sharply reduces the consumption of collecting reagent, although the reduction does not ap pear to be directly proportional to the reduction in specific surface: Likewise,-the reduction, in

- flotation time provides for economy in flotation cell equipment.-

It is accordingly a purpose to separate from.

the ground materials the maximum proportions,

in increasing order of particle sizes, that may be recombined with the flotation tailings, derived from the coarser fractions without afl'ecting the chemical composition desired for burning.

The material of this example was metamorphosed limestone, referred to asthe Conestoga formation, but probably of the Jack'sonburg for- Its chemical composition is generally.

mation'. equivalent to the materials previously described,

but only a trace'of carbonaceous matter is present, too little to affect froth flotation.- A principal mineralogical diflerence is that a substantial proportion of the magnesia is combined as phlogopite mica, although the most abundant silicate is sericite mica. Natural crystallization is much coarser, the broken rock presenting mica shist on the bedding-plane surfaces, in overlapping flakes along the planes. The edges reveal relatively coarse calcite and quartz crystals between the planes, but the crystals are too fine for identification except by petrographic examination.-

A sample of this material, the composition of which will 'be given hereinafter, was ground to a'fineness of 88% minus the 200 mesh sieve, with "72% minus the 325 mesh sieve, at which degree of fineness a sufllcient proportion of free mica was present in the coarser fractions to permit the desired correction.

The ground material was diluted to 15.7% dry solids. and dispersed with 2.5 lbs. of calcium lignin sulphonate per tons of solids, to reduce natural flocculation, whereby effective classification could be made to-separate the finer slimes. The quantity of this agent required to complete dispersion can usually be materially reduced by adding it to the pulp with about 1 1b. of soda ash per ton of solids, as described more fully in the 'co-pendin'g application of Breerwood Serial No.

163,303, flled.September 10, 1937.

After dispersion, the pulp was hydraulically classified to separate the finer slimes from the' coarser fractions, hereinafter called sands", the particle size separation having been made at 20 It will be seen that the increased in the sands. I

The sands were subjected to flotation to effect proportion ofquartz the necessary reduction, particularly in alumina and also in total silica, whereby the flotation tailings in direct recombination with the untreated fines wouldprovide a satisfactory mixture, withthe addition of avery small quantity of high grade silica. with allowance for coal ash correction.

The'pulp was then diluted to 20% dry solids and subjected to froth flotation in the presence of 0.05 lb. of positive ion reagent 0-2 in dilute aqueous solution and 0.027 lb. of frothin'g agent F-l per ton of flotation feed only. Rougher flotation was completed in 3 minutes. The pulp temperature was 70 F. and alkalinity was normal at pH 7.8.

The results of flotation were as follows:

Pep Analyses as percent- No Product cent s10, reio, Aho, caco.

Flotation ieed 100.0 17:48 2.16 5.05 68.20

l. Rougher conc. 16.5 53.00 2.79 9.58 12.72 2 Rougher tails... 83.5 11.71 2.10 302 mm i"iis+s1ii-.e s 89.77 an 1.93 1.25 7 6.8

It is especially to be noted that about 56% of the alumina available in the flotation feed .was concentrated in only 16% of the weight of the feed. The combination of the untreated slimes with the rougher tailings provided a total weight recovery of nearly of the originalmaterials and it will be evident that the addition of one or two percent of-high grade silica would effect the ultimate correction more economically than omy in positive ion reagent consumption is a primary object ofthe invention, and it will be seen that by treating a limited proportion of the total available materials, as described above, the consumption of this reagent with relation to the original supply was only 0.031 lb. per ton.

We claim:

1. In the method ofbeneficiating, for .the preparation of an ultimate cement raw material mixture, inferior cement raw materials containing at least two of the constituents essential to an ultimate cement raw material mixture and including an amount of at least one siliceous mineral in excess of that desired in the ultimate mixture, to reduce the percentage of said siliceous mineral; the improvement which comprises subjecting a pulp of the ground'material to frothfiotation in the presence of an amount of a reagent, the surface-active portion of which is a ositive ion having selective collecting capacity for the constituents of the naturally occurring raw materials including'said siliceous mineral,

sufficient to collect the excess proportion of= said siliceous mineral, but insufficient in amountto collect all of the normally floatable portion of said siliceous constituent, to concentrate a minimum of the weight of said material in the froth,

whereby the excess of said siliceous 'mineral is carried oif in the froth.

2. In the method of beneficiating, for the preparation of an ultimate cement raw material mixture, inferior cement raw materials containing at least two of the constituents essential to --an ultimate cement raw. material mixture and including an amount of at least .one silicate mineral in excess of that desired in the ultimate mixture, to reduce the percentage of said silicate mineral; the improvement which comprises, subjectingj a pulp of the ground material to froth flotation in the presence of an amount of a. reagent, the .surface-active portion of which is a positive ion having selective collecting capacity for the constit uents of the naturally occurring raw materials including siliceous minerals, sumcient to collect the excess proportion of said silicate mineral, but insuflicient in amount to collect all of the normally floatable portion of said constituents, to concentrate a minimum of the weight/of said material in the froth, whereby the excessof said silicate mineral is carried oil in the froth.

3. In the method of beneficiating, for the preparation of an ultimate cement raw material mixture, inferior cement raw materials containing at leasttwo of the constituents. essential to an ultimate cement raw material mixture and including an amount of at least one silicate mineral in excess of that desired in the ultimate mixture and a proportion of silica desired for said mixture, to reduce the percentage of said silicate mineral and increase the percentage of silica; the

elicess proportion of said silicate mineral, but

portion of silica, to concentrate afminimum of the weight of said material in the froth, whereby the excess of the silicate mineral is carried off in the froth, and the proportion ,of. silicate mineral in the tailings is reduced andthe proportion of silica therein is increased. I Y 4. In the method of beneflciating, for the preparation of an ultimate cement raw material mixture, inferior cement raw materials containing at least two of the constituents essential to an ultimate cement raw material mixture and ineluding an amount'of micaceous matter in excess and a proportion of silica desired for said mixture, to reduce the percentage of said micac'eous matter provement which comprises subjecting a pulp of the ground material to froth flotation in the presence of an amount of a reagent, the surface-,

lectthe excess proportion of the micaceous matter, but insufflcient in-amount to collect a'substantial proportion of the silica, to concentrate a of the weight of said material in the froth, whereby'the excess of micaceous matter is carried off 'in the froth and the proportion of .micaceous matter in the tailings is reduced and the proportion of silica therein is increased.

5. 'In the method of beneflciating;,for the preparation of an ultimate cement raw material mixand increase the percentage of silica; the 1m-.

ture, inferior cement raw materials of the class argillaceous lim'estones, marls and chalks, which contain an amount of micaceous matter in excess of that desired in the ultimate mixture and a proportion of silica'desired for said mixture, to

reduce the percentage of micaceous matter and ,increase the percentage of silica; the improve- -ment which comprises subjecting a pulp of the ground material to froth flotation in the presence of an amount of a reagent; the surface-active portion of which is a positive ion having differential selective collecting capacity for siliceous'minerals and calcite of the naturally occurring raw materials, suflicient to collect the excess of micaceous material, but insuflicient to collect all of the normally floatable portion of said constituents, and insuflicient to collect'a'substantial proportion of the silica and calcite, to concentrate a minimum of the weight of said material in the froth, whereby the excess of micaceous matter is eral in excess of that desired in the ultimate mixture, toreduce the percentage of said siliceous mineral; the improvement which comprises subjecting-a pulp of the ground material to froth flotation in the presence of an amount of a re-' agent, the surface-active portion of which is a positive ion having differential selective collectingcapacity for siliceous minerals and calcite. of the naturally occurring raw materials, suflicient to collect the excess of siliceous mineral, but'insumcient in amount to collect a. substantial proportion of the calcite, to'concentrate a minimum of the weight of the material in the froth,-whereture, inferior cement raw materials of the class argillaceous limestones, marls and chalks, which contain an amount of at leastone siliceous mineral in excess of that desired in the ultimate mixture, to reduce the percentage of said siliceous mineral; the improvement which comprises classlfying a ground supplyof the material to separate a part comprising the finer fractions from a part comprising the coarser fractions, subjecting a pulp of one of the separated parts to froth flotation in the presence of an amount of 'a reagent, the surface-active portion of which is a positive ion having differential selective collecting capacity for siliceous minerals and calcite of the naturally'occurring raw materials,-

sufilcient to collect thev excess of siliceous mineral, but insufiicientin amount to collect a substantial proportion of the calcite, to concentrate a minimum of the weight of said pulp in the froth, whereby the excess of siliceous mineral is carried off in the -froth and the proportion of the siliceous mineral in the tailings is reduced-and the proportion of calcite therein is increased.

mineral by subtracting the excess from a fraction of the materials comprising the coarser particles and re-combining the remainder of thefraction with a fraction comprising the finer particle sizes; the improvement which comprises classifying a ground supply of the material to separate a part comprising the finer fractions from a part comprising the coarser fractions, subjecting a'pulpof Y the coarse part to frothfiotation' in" the presence of an amount of a reagent, the surface active ous mineral, but insufficient in amount to collect portion of which-is a positive ion having diiferential selective collecting capacity for siliceous minerals and calcite of the naturally occurring raw materials, sufiicient to collect the excess of silicea substantial proportion of the calcite, to concentrate a minimum of the weight of said pulpin the froth, whereby the excess of siliceous mineral is carried ofi in the froth and the proportion of siliceous mineral in thetailings is reduced and the proportion of calcite therein is increased.

9; In the method of beneficiating, for the preparation of an ultimate cement raw material mixture, inferiorcement raw materials-of the class argillaceous limestones, marls and chalks, which contain an amountof at least one siliceous mineralin excess of that desired in' the ultimate mixture, to reduce the percentage'of said siliceous mineral by subtracting the excess from a frac-- tion of the materials comprising the coarser particles; the improvement which comprises classify-, ing a ground supply of the material to separate a part comprising at least the finest slimes from a part comprising the coarser particle's, subjecting a pulp of the coarser part to froth'fiotation in the presence of an amount of a'reagent, the

surface-active portion of whichfis a positive ion having differential selective'collecting capacity.

8. In the method ojbeneficiating, for the prep for siliceous minerals and calcite of the naturally occurring raw materials, sufllcient to collect the excess of siliceous mineral, but insuflicient in amount to collect a substantial proportion of aration of an ultimate cement raw material mixture, inferior cement raw materials of the class argillaceous limestones, marls and chalks, which contain an amount of at least one siliceous mineral in excess of that desired in the ultimate mix-' ture, to reduce the percentage of said siliceous mineral by subtracting the excess from a fraction of the materials comprising the coarser particles; the improvementwhichcomprises classifying a ground supplyof the material to separate a part comprising at least the finest slimes from a part comprising the coarser particles, subjecting a pulp of the coarser part to rougher froth flotation in the presence of an amount of a reagent, the surface active portion of which is a' positive ion having differential selective collecting capacity for siliceous minerals and calcite 01' the naturally occurring raw materials, suflicient to collect the excess of siliceous mineral, but in-.-' sufiioient to, collect all of the normally fioatable portion of said siliceous constituent and insufiicient to collecta substantial proportion of the calcite,;to concentrate a minimum of the weight,-

of the pulp in the froth; subjecting the rougher concentrates to froth flotation to clean the concentrat es of useful quantities of minerals, whereby the excess of said siliceous mineral is carried ofi in the cleaned froth,

11. In the method oi, beneficiating, for the preparation of an ultimate cement raw material mix ture, inferior cement raw materials of the class argillaceous limestones, marls and chalks, which contain an amount of at least one siliceous mineral in excess of that desired in the ultimate mixture, to reduce the percentage of said siliceous mineral; the improvement which comprises conditioning a pulp of the ground raw material containing an abundance of fine slimes in the presenceoii a dispersing agent to reduce natural flocculation, classifying the conditioned pulp to separate a quantity comprising at least thefinest slimes, subjecting the remainder of the pulp to froth flotation in the presence of an amount of a reagent, the surface-active portion of which is a positive ion having differential selective collecting capacity for siliceous minerals and calcite of the naturally occurring raw materials, 'suiiicient to collect the excess ot-siliceous mineral, but in sumcient in amount to-collect a substantial proportion or the calcite, to concentrate a minimum of the weight of the material inthe froth, whereby '-'the excess of siliceous mineral is carrieclofi-in the froth and the proportion of siliceous mineral in the ,tailings is reduced and the proportion of calcitetherein is increased.

12. In the method of beneficiating, for the preparation of an ultimate cement raw material mixture, inferior cement raw materials of ,the class argillaceous limestones, marls 'ar'id chalks, which contain an amount "of at least one sliceous mineral in excess of that desired in the ultimate mixture, to reduce the percentage of said siliceous mineral; the improvement which comprises conditioning a pulp of the ground raw material containing an abundance of fine slimes in the presence of a dispersing agent to reduce natural flocculation, subjecting the conditioned pulp to froth flotation in the presence of an amount of a re-. agent, the surface-active portion of which is a positive ion having differential selective collecting capacity for siliceous minerals and calcite of the naturally occurring raw,materials, suflicient to collect the excess of siliceous mineral, but insufiicient in amount to collect a substantial proportion of the calcite, to concentrate a minimum of the weight of the material in the froth, whereby the excess of siliceous mineral is carried off in the froth and the proportion of siliceous mineral in the tailings is reduced and the proportion of calcite therein is increased.

13. In the method of beneflciating, for the preparation of an ultimate cement raw material mixture, inferior cement raw materials of the class argillaceous limestones, marls and chalks,

which contain an amount of at least one siliceous mineral in excess of that desired in the ultimate mixture, to reduce the percentage of said siliceous mineral; the improvement which comprises conditioning a pulp of the ground raw material containing an abundance of fine slimes in the presence of a dispersing agent to reduce natural flocculation, subjecting the conditioned pulp to froth flotation in a light stage oilingcircuit in the presence of amounts of a reagent, added in increments to the pulp in said circuit, the surface-active portion of the reagent being a positive ion having diflerential selective collecting capacity for siliceous minerals and calcite, the

total amount of the reagent being suflicient to" collect the excess of siliceous mineral, each amount so added being insufiicient to concentrate a substantial proportion of the calcite, to concentrate a minimum of the weight of the material in the froth, whereby the excess of siliceous mineral is carried off in the froth and the proportion of siliceous mineral in the tailings is reduced and the proportion of calcite therein is increased.

14. In the method of beneficiating, for the preparation of an ultimate cement raw material mixture, inferior cement raw materials of the class argillateouslimestones, marls and chalks,

which contain an amount of at least one siliceous mineral in excess of that desired in the ultimate mixture, to reduce the percentage of said siliceous mineral; the improvement which comprises subjecting a pulp of the ground material to froth flotation in thepresence of an amount of a reagent, the surface-active portion of which is a positive ion containing an aliphatic hydrocarbon group of at least eight carbon atoms, said ion having differential selective collecting capacity for siliceous minerals and calcite of the naturally occurring raw materials, sufiicient to collect theexcess of siliceous mineral, but insufficient in amount to collect a substantial proportion of the 15. In the method 'of beneficiating, for. the

preparation of an ultimate cement raw material mixture, inferio; cement raw materials of the class argillaceous limestones, marls and chalks, which contain an amount of at least one silliceous mineral inexcess of that desired in the ultimate mixture, to reduce the percentage of said siliceous mineral; the improvement which compris'essubjecting a pulp of the ground material to froth flotation in the presence of an amount of a reagent, of a class quaternary ammonium compounds containing a hydrocarbon group of from twelve to eighteen carbon atoms, wherein the constituents in solution give-a positively charged ion having dif.erential selective collecting capacity for siliceous minerals and calcite of the naturally occurring raw materials, sufficient to collect the excess of siliceous mineral, but insufiicient in amount to collect a substantial propor tion of the calcite, to concentrate a minimum of the weight of the material in the froth, whereby the excess of siliceous mineral is carried off in the froth and the proportion in the tailings is reduced and the proportion of calcite therein is increased.

16. In the method of beneflciating, for the preparation of an ultimate cement raw material mixture, inferior cement raw materials of the class argillaceous limestones, marls and chalks pounds containing a: hydrocarbon group-of from twelve to eighteen carbon atoms, wherein the constituents in solution give a positively charged,

ion having differential selective collecting capacity for siliceous minerals and'calcite of the naturally occurring raw -.materials,,the negative ion in solution being a halogen, 'suflicient' to collect the excess of siliceous mineral, but ins'uflicient to collect a substantial proportion of the calcite,

to concentrate a minimum of the weight of the material in the froth, whereby the excess of siliceous mineral is carried off in the froth and the proportion in the tailings is reduced and the proportion of calcite therein is increased.

17. In the method of beneficiating, for the preparation of an ultimate cement raw material -mixture, inferior cement raw materials of the class argillaceous limestones, marls and chalks, which contain an amount of at least one siliceous mineral in excess of that desired in the ultimate mixture, to reduce the percentage of said siliceous mineral; the improvement which comprises subjecting a pulp of the ground material to froth flotation in the presence of an amount of dodecyl amine hydrochloride sufficient to collect the excess of siliceous mineral, but insufficient in amount to collect a substantial proportion of the calcite, to concentrate a minimum of the weight of the material in the froth, whereby the excess of siliceous mineral is carried off in the froth and the proportion ofthe siliceous mineral in the tailings is reduced and the proportion of calcite therein is increased.

18. In the method of' beneficiating, for the preparation of an ultimate cement raw material mixture, inferior cement raw materials of the class'argillaceous limestones, marls and chalks,-

which contain an amount ofv at least one siliceous mineral in excess of that desired in the ultimate mixture, to reduce the percentage of said siliceousv mineral; the improvementwhich comprises subjecting a pulp of the groundmaterial to froth flotation in the presence of .an amount of a' mix-- ture of hydrochlorides of the higher primaryaliphatic amines in which the'alkyl groups corincreased.

mineral is carried off in the froth and the proportion of the siliceous mineral in the tailings is reduced and the proportion of calcite therein is CHARLES H. BREERWOOD. JOHN C. WILLIAMS. 

